No, it's not a Country area model - it has a route number. It is alpha-coded. Unfortunately it's stored out of easy reach at present and I haven't looked at it for some time. I was quite sure it had "R" as a classification but now you mention "C/M" I'm not so sure. I'll try to get it out as take a look.
I understand that London Country's Gibson machines went back to LT in the early / mid 70s, as by that time LC's OPO drivers were using Almex machines, and after (almost all) the Green Line routes had gone OPO, the Setrights were cascaded to the remaining crew operated bus routes.
Some were used for spares, others did go back in to service - they could sometimes be spotted because the print plate didn't always include the word 'ROUTE' above the route number after they had been converted to print a route number rather than the date. (I have read somewhere that there was an idea of using machines that showed the date for an on-bus 'all day' ticket on the short lived Shop Linker route, but I don't think this ever happened.)
Yours could be a converted country bus machine, and it might not have seemed worth converting it so it could show one obsolete class code rather than another, but that would certainly make yours a rarity.
I'm fairly sure I never got, and have not seen a central bus Gibson ticket (other than pictures of tickets from prototypes), showing 'R' class (very occasionally a conductor would issue tickets showing C/M or EMS through being careless or silly) but that doesn't prove it wasn't possible with some machines.
And as an aside, with any ticket machine, it's worth having a bit of a play with it now and then to stop moving parts getting stuck - I now can't change the route number on my Gibson...